1. Field of the Invention
The present invention relates to a dry etching method in which an end point of the etching is detected when etching a film formed on a substrate. Also, the present invention relates to an etching method for forming an active layer comprising silicon and electrodes comprising metal of a semiconductor device, such as a thin film transistor.
2. Description of the Related Art
In a process of producing a semiconductor device such as an LSI, a super LSI or a thin-film transistor (TFT), an etching process is conducted for making a film formed on a substrate into a desired shape. The etching process may be conducted by dry etching, wet etching or the like. One of general TFT structures and one of methods for fabricating thin film transistors are disclosed in U.S. Pat. No. 5,534,716. The entire disclosure of U.S. Pat. No. 5,534,716 including specification, claims, drawings and summary are incorporated herein by reference in its entirety.
A method most used for detecting the end point of the etching in the dry etching is a spectrochemical analyzing method. In this method, the end point of the etching is judged by allowing a spectrum emitted from a reaction product of an etching gas in plasma or a reaction product of a film to be etched to pass through a spectroscope or the like to read a variation in the intensity of light emission.
However, there is a case in which the end point of the etching can not be detected because the variation in the intensity of light emission is small depending on the light emission species from which the spectrum for detecting the end point of the etching is emitted. Also, there is a case in which the end point of the etching can not be detected because a wavelength to be spectrochemically analyzed is superimposed on another wavelength depending on the combination of a film to be etched with an etching gas.
In addition, there arises such a problem that the detection of the end point high in accuracy and excellent in reproducibility can not be performed because the reaction product is deposited on a window defined in the reaction chamber for detecting the spectrum to make the intensity of a light that passes through the window low.
In particular, as the high integration of the semiconductor devices is progressed, it becomes important that the end point of the etching is accurately caught in order to form a fine pattern high in accuracy with an excellent reproducibility.
The present invention has been made in order to solve the above-mentioned problems, and therefore has an object of the present invention to detect an end point of the etching high in accuracy and excellent in reproducibility.
According to one aspect of the present invention disclosed in the present specification, there is provided a method of etching a film formed on a substrate by dry etching, characterized by comprising the steps of: measuring a variation in a self-bias voltage, and setting a time point when the variation in the self-bias voltage comes to a fixed value as an end point of the etching.
Further, in the above-mentioned structure, it is characterized in that the time point when the variation in the self-bias voltage comes to the fixed value is a time point when a differentiation value becomes 0 if the variation in the self-bias voltage is differentiated.
According to another aspect of the present invention, there is provided a method of etching a film formed on a substrate by dry etching, comprising the steps of:
measuring a light emission from a light emission species existing in a reaction chamber during etching and a variation in a self-bias voltage; and
setting a time period when a difference between the self-bias voltage and the intensity of the light emission becomes a fixed value as an end point of the etching.
Also, in the above-mentioned structure, it is characterized in that the time point when the difference comes to the fixed value is a time point when a differentiation value becomes 0 if a variation in the difference between the self-bias voltage and the intensity of the light emission is differentiated.
Further, an etching device according to another aspect of the present invention comprises:
an anode and a cathode disposed in a reaction chamber;
a high-frequency power supply connected to the cathode through a matching box; and
a voltmeter connected to the cathode for measuring a self-bias voltage;
characterized in that the self-bias voltage is monitored by the voltmeter to detect an end point of the etching.
Also, an etching device according to further another aspect of the present invention comprises:
an anode and a cathode disposed in a reaction chamber;
a high-frequency power supply connected to the cathode through a matching box;
a voltmeter connected to the cathode for measuring a self-bias voltage;
a window disposed within the reaction chamber; and
a detector for detecting a light emission of a light emission species occurring within the reaction chamber through the window via a spectroscope;
characterized in that a difference between the intensity of the light emission and the self-bias voltage is monitored by the voltmeter to detect an end point of the etching.